If this is actually your issue, you may kick yourself ...
I think this may be just because you are "installing" and not "upgrading"
replace -ih
with -Uh
I created a test RPM with similar setup, here are the results:
With -ih as you did
$ sudo rpm --prefix ~/rpmroot/ -ih /home/nhed/rpmbuild/RPMS/x86_64/ptst-1.1.0-1.x86_64.rpm
##################################### [100%] file /home/nhed/rpmroot/etc/a from install of ptst-1.1.0-1.x86_64 conflictswith file from package ptst-1.0.0-1.x86_64 file /home/nhed/rpmroot/etc/b from install of ptst-1.1.0-1.x86_64 conflicts with file from package ptst-1.0.0-1.x86_64 file /home/nhed/rpmroot/etc/c from install of ptst-1.1.0-1.x86_64 conflicts with file from package ptst-1.0.0-1.x86_64
With -Uh
$ sudo rpm --prefix ~/rpmroot/ -Uh /home/nhed/rpmbuild/RPMS/x86_64/ptst-1.1.0-1.x86_64.rpm
##################################### [100%]warning: /home/nhed/rpmroot/etc/a created as /home/nhed/rpmroot/etc/a.rpmnew
##################################### [100%]